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## Work in thermodynamics

For a mechanical system, work is the action of a force on an object through some distance.

In a thermodynamic system, work by a system is the energy transferred by the system to the surroundings.

A thermodynamic system can exert force of

the surrounding to push or displace it through some distance. For example, the gas molecules hitting the boundary of the container and displacing it. Consider the adjacent figure. The sum of all F.ΔS over the whole boundary is the work done by the system on its surroundings. By convention, work done by the system is considered positive and work done on the system as negative.

IN PHYSICS, A CONVENTION IS A GENERALLY ACCEPTED RULE, PROBABLY HAVING NO SCIENTIFIC OR MATHEMATICAL PROOF. FOR EXAMPLE, CHARGE ON AN ELECTRON IS TAKEN NEGATIVE. IF INITIALLY, IT WAS IT WAS ASSUMED TO BE POSITIVE, WE WOULD NOW BE USING IT POSITIVE WITHOUT ANY PROBLEMS.

## Internal Energy

Matter consists of atoms or molecules which are in the state of continuous motion.

• Atoms in solids continuously vibrate back and forth about their equilibrium positions.
• Molecules of liquids continuously move around. They collide with one another and exchange energies.
• Molecules of gases continuously move about and have frequent elastic collision with one another.

The K.E is contributed by the translational, rotational or vibrational motion of the particles.
Similarly, the potential energy is due to the relative positions of molecules/atoms due to the intermolecular forces of the syste

Internal energy is the total amount of kinetic energy and potential energy of all the particles in the system.

Quiz
The temperature of a normal healthy person is 37°. What will be the temperature of a dead body?
Think about a hot cup of tea placed on table before you. It will slowly cool until the room temperature. A dead body, like any non-living thing, will cool to the temperature of the surroundings. However, it is found that in normal cases, it cools down 0.83° C in an hour.

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